Robust Allocation of Operating Rooms: a Cutting Plane Approach to handle Lognormal Case Durations

Please always quote using this URN: urn:nbn:de:0297-zib-58502
  • The problem of allocating operating rooms (OR) to surgical cases is a challenging task, involving both combinatorial aspects and uncertainty handling. We formulate this problem as a parallel machines scheduling problem, in which job durations follow a lognormal distribution, and a fixed assignment of jobs to machines must be computed. We propose a cutting-plane approach to solve the robust counterpart of this optimization problem. To this end, we develop an algorithm based on fixed-point iterations that identifies worst-case scenarios and generates cut inequalities. The main result of this article uses Hilbert's projective geometry to prove the convergence of this procedure under mild conditions. We also propose two exact solution methods for a similar problem, but with a polyhedral uncertainty set, for which only approximation approaches were known. Our model can be extended to balance the load over several planning periods in a rolling horizon. We present extensive numerical experiments for instances based on real data from a major hospital in Berlin. In particular, we find that: (i) our approach performs well compared to a previous model that ignored the distribution of case durations; (ii) compared to an alternative stochastic programming approach, robust optimization yields solutions that are more robust against uncertainty, at a small price in terms of average cost; (iii) the \emph{longest expected processing time first} (LEPT) heuristic performs well and efficiently protects against extreme scenarios, but only if a good prediction model for the durations is available. Finally, we draw a number of managerial implications from these observations.

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Author:Guillaume Sagnol, Christoph Barner, Ralf Borndörfer, Mickaël Grima, Matthes Seeling, Claudia Spies, Klaus Wernecke
Document Type:ZIB-Report
Tag:Hilbert's projective metric; lognormal duration; robust optimization
MSC-Classification:90-XX OPERATIONS RESEARCH, MATHEMATICAL PROGRAMMING / 90Cxx Mathematical programming [See also 49Mxx, 65Kxx]
Date of first Publication:2016/03/24
Series (Serial Number):ZIB-Report (16-18)
Published in:Appeared in: European Journal of Operational Research 271(2):420-435